Interleukin-12 (IL12) is a pro-inflammatory cytokine that plays an important role in innate and adaptive immunity. Gately, M K et al., Annu Rev Immunol. 16: 495-521 (1998). IL12 functions primarily as a 70 kDa heterodimeric protein consisting of two disulfide-linked p35 and p40 subunits. IL12 p40 homodimers do exist, but other than functioning as an antagonist that binds the IL12 receptor, they do not appear to mediate a biologic response. Id. The precursor form of the IL12 p40 subunit (NM_002187; P29460; also referred to as IL12B, natural killer cell stimulatory factor 2, cytotoxic lymphocyte maturation factor 2) is 328 amino acids in length, while its mature form is 306 amino acids long. The precursor form of the IL12 p35 subunit (NM_000882; P29459; also referred to as IL12A, natural killer cell stimulatory factor 1, cytotoxic lymphocyte maturation factor 1) is 219 amino acids in length and the mature form is 197 amino acids long. Id. The genes for the IL12 p35 and p40 subunits reside on different chromosomes and are regulated independently of each other. Gately, M K et al., Annu Rev Immunol. 16: 495-521 (1998). Many different immune cells (e.g., dendritic cells, macrophages, monocytes, neutrophils, and B cells) produce IL12 upon antigenic stimuli. The active IL12 heterodimer is formed following protein synthesis. Id.
Due to its ability to activate both NK cells and cytotoxic T cells, IL12 protein has been studied as a promising anti-cancer therapeutic since 1994. See Nastala, C. L. et al., J Immunol 153: 1697-1706 (1994). But despite high expectations, early clinical studies did not yield satisfactory results. Lasek W. et al., Cancer Immunol Immunother 63: 419-435, 424 (2014). Repeated administration of IL12, in most patients, led to adaptive response and a progressive decline of IL12-induced interferon gamma (IFN-γ) levels in blood. Id. Moreover, while it was recognized that IL12-induced anti-cancer activity is largely mediated by the secondary secretion of IFNγ, the concomitant induction of IFN-γ along with other cytokines (e.g., TNF-α) or chemokines (IP-10 or MIG) by IL12 caused severe toxicity. Id.
In addition to the negative feedback and toxicity, the marginal efficacy of the IL12 therapy in clinical settings may be caused by the strong immunosuppressive environment in humans. Id. To minimize IFN-γ toxicity and improve IL12 efficacy, scientists tried different approaches, such as different dose and time protocols for IL12 therapy. See Sacco, S. et al., Blood 90: 4473-4479 (1997); Leonard, J. P. et al., Blood 90: 2541-2548 (1997); Coughlin, C. M. et al., Cancer Res. 57: 2460-2467 (1997); Asselin-Paturel, C. et al., Cancer 91: 113-122 (2001); and Saudemont, A. et al., Leukemia 16: 1637-1644 (2002). Nonetheless, these approaches have not significantly impacted patient survival. Kang, W. K., et al., Human Gene Therapy 12: 671-684 (2001).
Currently, a number of IL12 clinical trials are on-going. Though these multiple clinical trials have been on-going for nearly 20 years since the first human clinical trial of IL12 in 1996, an FDA-approved IL12 product is still not available. Thus, there is a need in the art for an improved therapeutic approach for using IL12 to treat tumors.